Laser ablation is a common surgical technique for removing unwanted matter. For example, in heart surgery, laser ablation is used to remove blockages. However, the use of laser ablation is usually limited to applications where the distinction between matter to be retained and matter to be removed is easily discernible so the laser may be precisely directed. Otherwise, misdirected laser energy may remove or damage matter that should be retained.
In orthopedics, when securing a pin to bone, it is desirable to ensure that the pin is actually being cemented to bone and not to other matter. Polymethyl methacrylate (PMMA) is often used as an adhesive for securing metal pins to bone. When securing a pin to bone, it is desirable to ensure that any remaining PMMA from a previously-installed pin is removed and that the pin is being secured to bone and not to soft tissue, dead bone, or to infected or otherwise unhealthy bone. All unwanted matter must be removed while minimizing the removal of healthy bone.
When a pin that was previously cemented into bone using PMMA is later removed, some PMMA is left behind in the cavity from which the pin was removed. A surgeon may use an arthroscope to look down into the cavity as a visual guide for the surgeon's attempts to remove the PMMA from the surface of the bone. However, looking through an arthroscope, it is difficult to distinguish between PMMA and bone because they are similar in color and because the arthroscope has limited resolution. In some orthopedic procedures, the old PMMA is liquefied to remove the previously-cemented pin and the liquefied PMMA is absorbed into the bone, making the distinction between bone and PMMA more difficult to see.
The difficulty in distinguishing between matter to be removed and matter to be retained makes use of laser ablation or other methods of removal (e.g., scalpel, ultrasound) problematic for orthopedics. Misdirected laser energy, for example, can penetrate bone and remove or damage bone at locations where healthy bone is desired.
Fourier transform infrared (FTIR) spectroscopy techniques may be used to identify materials by measuring their absorption spectra. This technique includes the time consuming steps of taking a biopsy of the sample material, forming a solution of the sample material, and analyzing the solution with a spectrometer. However, the use of FTIR is not practical in a surgical setting where real-time analysis is required because the steps described above are time consuming and must be repeated for each location to be tested. An improved method and apparatus are needed for distinguishing between materials in real time and/or in a harsh surgical environment where contaminants such as bodily fluids are present and visibility may be limited.